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Scratchbuild Contest # 2 Enty: "Gronk" 36" span, 20 gram, Indoor RC Flying Wing

Old 11-03-2008, 03:46 AM
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The Don
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Default Scratchbuild Contest # 2 Enty: "Gronk" 36" span, 20 gram, Indoor RC Flying Wing

Here is my official build thread for "Gronk"

Specs:
wingspan: ~36"
approx finished weight: 20 grams
radio: Parkzone vapor brick
lipo: 1S 70 mah lipo


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Last edited by The Don; 11-10-2008 at 04:56 AM.
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Old 11-03-2008, 03:50 AM
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Here are some build photos. The wing spars are 1/16 x 1/8" 6-7 lb density balsa. The ribs are cut from a sheet of .040" balsa that is about 6 pound density as well. The airfoil is a 5% simplex.

More photos to come as I glue it all together.

Don
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Old 11-03-2008, 04:57 AM
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That is the plan. The free flight version was 17 grams and had two 50 mah nicads for power.

Here are some more photos.

#1 cut our the diagonal ribs.
#2 general layout of all ribs in place
#3 cut out of the trailing edge pieces of the elevons.

I forgot to mention how the controls will work. This will be an elevator rudder model. The elevons will be mounted and fixed with the correct amount of relfex needed for level flight. The center section will have its own elevator on the trailing edge which can go up and down for pitch control. The reason this was done is that I do not believe the tiny linear servos on the Vapor brick can handle such large elevons. I have not posted the side view yet so you have not seen the upper and lower rudders but they will provide the yaw control combined with the dihedral inthe wing will give me directional control

In essence it will be trimmed as a free flight model yet I will still have control to guide it. I wont be doing loops or rolls but that is not the purpose of this model.


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Old 11-04-2008, 04:10 AM
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Started my wing construction.
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Old 11-04-2008, 05:21 AM
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Thanks! Here is a new photo I added the diagonal ribs. That is all for tonight.

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Old 11-04-2008, 06:13 AM
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I have not decided yet. My free flight version was covered with condenser paper which is the paper they use in winding paper capacitors. That paper is about .35 grams per 100 square inches. The problem I had on the free flight version was the wings would sometimes twist when it hit a bump of air so I had to brace the wing to stabilize it. This one I am making now has the diagonal ribs which add to the torsional stiffness. If I also cover with Esaki tissue, then the stiffness will be much higher as well. But the weight is much higher, about 1 gram per 100 sq inches, and i need abotu 300 square inches of covering.

My other option is to cover it with clear plastic film like I use on my normal indoor free flight models. I have some film which will work that weighs about .12 grams per 100 square inches. If I go this route the wing will have to have external bracing. So I am still up in the air. I wanted to have an unbraced wing design, so may go the tissue route with the weight penalty. Plus I have many colors of tissue to give it some color. Tomorrow I will take the wing off the board, and weight it and see where I am weight wise and see how it is in torsion then go from there.

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Old 11-07-2008, 04:42 AM
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Some more pictures and update. I made the elevons today. The weight of the wings and elevons as in the photo are 3.5 grams. I am doing good on tagret weight. Covering with tissue will be 3 more grams, so 6.5 grams. Then I have to do the body and fin, call it 2 more grams, so 8.5 grams then 10 for the radio, so that gets me to 18.5 grams so I think I will make 20 grams

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Old 11-07-2008, 09:57 PM
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This is actually heavy for me for this kind of building. Here is one of my lighter ones
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Old 11-09-2008, 08:04 PM
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More construction photos for you

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Old 11-09-2008, 08:07 PM
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A few more.
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Old 11-10-2008, 04:41 AM
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Thanks Larry!!! It is coming along good. I have decided to add gear so I can ROG in the gymnasium. Here are more photos.

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Old 11-12-2008, 03:37 AM
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Only a wicked light motor I think

Here are more photos, the airframe is complete, just need to install radio gear now. The weight is 9.4 grams without the radio gear. Looks like I will make my 20 grams

Don
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Old 11-13-2008, 05:32 AM
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Gronk is finished. Ready to fly weight is 20.14 grams

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Old 11-30-2008, 06:06 AM
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Gronk flies! Got a few flights in today. The gym was small and had all the heat vents blowing air straight down fom the ceiling which made flying quite difficult. This model has such a low airspeed that the down drafts would push one wing down and make the model circle to the right when I was going left. Here is a quick flight video.

[media]http://au.youtube.com/watch?v=xsO_SxRMgU0[/media]

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Old 01-02-2009, 12:48 AM
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I wanted to let you guys know I did the rudder modification and flew the wing last weekend. What a big difference it made. Rudder control is 100% better. I flew threee batteries worth of flights at the gym. I also dropped down to a singel cell 60 mah lipo and the AUW weight dropped down to about 18.5 grams and it helped the CG a little as well.

Here are some new photos.

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Old 02-15-2009, 04:34 AM
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We had another flying session tonight. I waited until near the end until the gym was down to 2 models. I put in an Eflite 110 mah lipo and got my best flight to date, 20 minutes and 26 seconds

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Old 02-15-2009, 04:43 AM
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20 minutes on 110 ma lipo! So your average amp draw is about .3 amps and a tad over 1 watt.

Thats some serious power you've got there Don. Very cool!
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Old 02-15-2009, 04:49 AM
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Did not think to look at it that way! At a 20 gram flying weight, looks like I am at ~28 watts per pound. A real power monster

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Old 02-15-2009, 05:53 AM
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Naw, thats only the average power. Id bet your peak power is probably 35 or maybe even 40 watts per pound
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